This invention relates to a stirrer roller developing device in an electrophotographic apparatus such as a copying machine and more particularly to a stirrer roller of a developing device having notches or holes in elliptical plates attached to its axis such that developing agent can be stirred evenly and dependably.
A common developing device for use in electrophotography in which a stirrer roller of the present invention may be used is illustrated in FIG. 4. With reference to FIG. 4, a photosensitive drum 1 and a developer roller 2 rotate in opposite directions as shown by respective arrows and a two-component developing agent 3 including carrier and toner converts latent images on the surface of the photosensitive drum 1 into visible images. Toner is supplied from a hopper 4 and a stirrer roller 5 is disposed behind the developer roller 2 to uniformly mix the supplied toner in the agent 3. As shown in FIGS. 5 and 6, a kind of stirrer roller previously considered is composed of a plurality of elliptical plates 6 affixed obliquely to an axis 7 at such angles that they are parallel to one another and appear as a circle when seen in the axial direction. With a stirrer roller of this type, the developing agent can be stirred satisfactorily in directions towards the peripheries but its axial motion remains local and the overall stirring of the toner supplied from the hopper 4 is not carried out efficiently. For this reason, a stirrer roller shown in FIGS. 7 through 9 has also been considered. This stirrer roller is different from the one shown in FIGS. 5 and 6 in that U-shaped notches 8 are provided to the elliptical plates 6 along their minor axes such that the developer agent 3 can easily move in axial direction and hence that the toner can be stirred more effectively as a whole. When this roller 5 rotates around its axis 7, however, the ring-like trajectories of these notches 8 become superposed one on top of another and the force tending to move the developing agent 3 toward the periphery becomes weak in such places, reducing the height of the developing agent (h in FIG. 4) locally. For this reason, the toner from the hopper 4 gathers at such places where the height of the developing agent is locally reduced and moves toward the developing roller 2 without becoming mixed uniformly. This tends to cause unevenness in the image density, thereby adversely affecting the image quality.